The following relates to the electrical power grid arts, electrical power grid frequency control arts, and related arts.
In conventional electrical power grid management, electrical power generation is controlled to match the current power demand. This approach requires making adequate provision for peak load by providing a source of excess power generating capacity, for example by providing ancillary generators that are brought on-line at peak demand hours. The excess power generating capacity is not used except during peak demand periods, and usually represents a net cost for the utility provider. Other approaches for matching generation to demand include shifting power between geographical grid regions, which again usually represents a net cost to the utility due to transmission line losses and so forth.
In demand response systems, loads (i.e. demand) are adjusted to match the available power generation. This approach can be cost effective since the utility can provide less excess power generating capacity. Commercial models for demand response systems typically include some incentive mechanism to induce load owners to participate in the demand response system. The Federal Energy Regulatory Commission (FERC) has codified incentivizing demand response systems in Order No. 745 issued March 2011, which mandates compensation for providers of demand response participating in the wholesale power marketplace.
By way of illustrative example, some demand response systems are described in Kirby & Staunton, “Technical Potential for Peak Load Management Programs in New Jersey”, Oak Ridge National Laboratory ORNL/TM-2002/271 (October 2002), and Kirby, “Spinning Reserve From Responsive Loads”, Oak Ridge National Laboratory ONRL/TM-2003/19 (March 2003). These references disclose loads operated as contingency reserves marketed on the day-ahead or hour-ahead markets. For example, spinning reserve may be provided using aggregations of air conditioners, water heaters, or so forth. A wireless communication network including the Internet is employed to send curtailment commands to thermostats which respond by taking immediate action or adjusting their schedules for future action. The thermostats send back data on temperature, set point, and power consumption. Thermostats can be addressed individually, in groups, or in total.
Brooks et al., “PG & E and Tesla Motors: Vehicle to Grid Demonstration and Evaluation Program, EVS23 (2007) discloses another illustrative example, in which an aggregation of loads in the form of electric vehicle battery chargers is leveraged to perform ancillary services for the grid, including frequency regulation based on an automatic generation control (AGC) signal. In a disclosed approach, a preferred operating point is defined, and the market value of regulation is based on deviations from this preferred operating point.
A difficulty with demand response systems is that the grid-level commands to adjust load draw (power or average energy over some time interval) can conflict with other limitations imposed on the loads. A common concern is interference with the intended use of the load. For example, operating an air conditioner continuously to provide increased draw can result in the air conditioned space becoming too cool; conversely, turning off the air conditioner for too long can result in the space becoming too hot. The use of an aggregation of loads can alleviate these problems, as loads can be prioritized to run (or not run) based on their current state, e.g. if increased draw is needed then those air conditioners whose thermostats are reading a high temperature are chosen to run first, before running air conditioners whose thermostats are reading a low temperature.
However, such load aggregation approaches cannot remediate other types of possible conflicts. For example, the call for increased demand may conflict with circuit-level limitations on current draw imposed by circuit breakers, or different types of ancillary services executing concurrently may also conflict. For example, a curtailment command (which requires reducing draw) may conflict with operation of the load for frequency regulation in which the automatic generation control (AGC) signal calls for increased draw to reduce a high grid frequency.
Disclosed herein are approaches for addressing such conflicts and/or other disadvantages of existing demand response systems employing load aggregation.